Screw fastener

ABSTRACT

A screw fastener includes a screwdriver that includes a sleeve having an absorption hole configured to absorb a top surface of a screw, a bit housed in the absorption hole and having a tip engageable with a recess of the screw, and a rotation unit configured to rotate the bit with the sleeve, a movement unit configured to move the screwdriver between a container configured to accommodate the screw and a work, a positional shift detector configured to detect a positional shift on a plane between a center axis of the screw perpendicular to the plane and a center axis of the bit perpendicular to the plane, and a controller controls a movement of the movement unit so as to reduce the positional shift, based on a detection result of the positional shift detector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. PCT/JP2008/053801, filed on Mar.4, 2008, the entire contents of which are incorporated herein byreference.

FIELD

The embodiment(s) discussed herein are related to a screw fastenerincluding a screwdriver configured to fasten a screw.

BACKGROUND

In automatic screw fastening, a screw is inserted into a screw hole in awork, and a screwdriver fastens the screw. If a member that inserts thescrew into the screw hole is the screwdriver itself, fastening canconveniently start just after the insertion. Accordingly, oneconventionally proposed method accommodates a screw in a tray on aworktable, picks up the screw engaged with a bit utilizing magnetism anda screwdriver, inserts the screw into a screw hole in a work, andfastens the screw.

In addition, this method previously memorizes a position of a centeraxis of the screw or a position of a center axis of a hole foraccommodating the screw, and moves the screwdriver so that the centeraxis of the bit can accord with the center axis of the screw.

Prior art include Patent Documents 1 and 2:

-   Patent Document 1: Japanese Laid-Open Patent Publication No.    3-221331.-   Patent Document 2: Japanese Laid-Open Utility Model Publication No.    5-60736.

Even if the screwdriver's movement is controlled so that the center axisof screwdriver's bit can accord with the center axis of the recess ofthe screw, a positional shift occurs between both center axes on a planeorthogonal to both center axes in actually positioning the bit due towear-out and changes with time of the motor and the transmissionmechanism. When the bit is engaged with the recess while both centeraxes shift from each other, the bit rubs on the recess. As aconsequence, the abrasion between the bit and the screw causes spread ofthe abrasion powder, and pollution and electric short circuit of theproduct. The deformation of the bit and the screw cause defective screwfastening with a predetermined torque, defective products, or anincreased number of tool exchanges, hindering the highly efficientproduction.

SUMMARY

Accordingly, it is an object in one aspect of the invention to provide ascrew fastener configured to prevent damages of a bit and a recess and ageneration of abrasion powder.

A screw fastener according to one aspect of the embodiment includes ascrewdriver that includes a sleeve having an absorption hole configuredto absorb a top surface of a screw, a bit housed in the absorption holeand having a tip engageable with a recess of the screw, and a rotationunit configured to rotate the bit with the sleeve, a movement unitconfigured to move the screwdriver between a container configured toaccommodate the screw and a work, a controller configured to controloperations of the screwdriver and the movement unit so as to pick up thescrew from the container and to fix a part onto the work with the screw,and a positional shift detector configured to detect a positional shifton a plane between a center axis of the screw perpendicular to the planeand a center axis of the bit perpendicular to the plane, wherein thecontroller controls a movement of the movement unit so as to reduce thepositional shift, based on a detection result of the positional shiftdetector.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a screw fastener of this embodiment.

FIGS. 2A and 2B are a sectional view and a top view of a screw placed ina container in the screw fastener illustrated in FIG. 1.

FIG. 3 is a sectional view of a screwdriver in the screw fastenerillustrated in FIG. 1.

FIGS. 4A and 4B are a sectional view and a bottom view of a lowerportion of a sleeve of the screwdriver illustrated in FIG. 3.

FIGS. 5A and 5B are a sectional view and a bottom view of the lowerportion of the sleeve that is located at a rotational position differentfrom FIG. 3.

FIGS. 6A and 6B are a sectional view and a bottom view of the lowerportion of the conventional screwdriver.

FIGS. 7A and 7B are a longitudinal sectional view and a cross sectionalview of the lower portion of the sleeve when the recess of the screwshifts from the groove of the sleeve while the sleeve illustrated inFIGS. 4A and 4B is located close to the top surface of the screw.

FIGS. 8A and 8B are a longitudinal sectional view and a cross sectionalview of the lower portion of the sleeve that is located at a rotationalposition different from FIGS. 7A and 7B.

FIG. 9 is an enlarged side view and a sectional view of an A part inFIG. 3.

FIG. 10 is a flowchart for explaining an operation of the screw fastenerillustrated in FIG. 1.

FIG. 11 is a flowchart for explaining the details of the step 1100illustrated in FIG. 10.

FIG. 12 is a flowchart for explaining the details of the step 1200illustrated in FIG. 10.

FIG. 13 is a sectional view of the lower portion of the sleeve in thestep 1220 illustrated in FIG. 12.

FIGS. 14A and 14B are a longitudinal sectional view and a crosssectional view of a lower portion of a sleeve according to a variationof FIGS. 7A and 7B.

FIGS. 15A and 14B are a longitudinal sectional view and a crosssectional view of a lower portion of a sleeve according to a variationof FIGS. 8A and 8B.

FIG. 16 is an enlarged plane view of a variation of FIG. 2B.

FIG. 17 is a partially enlarged sectional view of a lower portionaccording to a variation of the screwdriver illustrated in FIG. 3.

FIG. 18 is an exploded perspective view of essential componentsillustrated in FIG. 17.

FIG. 19 is a sectional view for explaining an operation of the screwfastener using the screwdriver illustrated in FIG. 17.

FIG. 20 is a variation of the flowchart illustrated in FIG. 11.

FIG. 21 is a variation of the flowchart illustrated in FIG. 12.

FIG. 22 is a plane view illustrating a positional shift between a grooveand a dent of a recess when there is a positional shift between a centeraxis of the recess of the screw and the center axis of the sleeve (bit).

FIG. 23 is a graph illustrating a relationship between the rotationalangle of the sleeve (bit) illustrated in FIG. 22 and an output of thevacuum monitoring detector.

FIG. 24 is a sectional view of a screwdriver according to a variation ofthe structure illustrated in FIG. 3.

FIGS. 25A and 25B are a longitudinal sectional view and a crosssectional view of the lower portion of the sleeve according to avariation of FIG. 4.

FIGS. 26A and 26B are a longitudinal sectional view and a crosssectional view of the lower portion of the sleeve according to avariation of FIG. 5.

FIGS. 27A and 27B are a longitudinal sectional view and a crosssectional view of the lower portion of the sleeve according to avariation of FIG. 7.

FIGS. 28A and 28B are a longitudinal sectional view and a crosssectional view of the lower portion of the sleeve according to avariation of FIG. 8.

DESCRIPTION OF EMBODIMENTS

A description will now be given of a screw fastener according to thisembodiment with reference to the accompanying drawing. FIG. 1 is a blockdiagram of a screw fastener 100. In FIG. 1, a lateral direction is an Xdirection, a longitudinal direction is a Y direction, and a directionperpendicular to the paper plane is a Z direction. FIG. 2A is apartially enlarged sectional view of a container 110. The screw fastener100 serves to pick up a screw and to fasten a part to a work W as anobject to be fastened using the screw, and includes a container 110, ascrewdriver 120, a movement unit 160, and a control system.

The container 110 is a tray placed on a worktable (not illustrated), andaccommodates one or more screws 10. The screws 10 are supplied one byone or in a lined-up matrix shape to container 110 by a screw supplier(not illustrated). Each screw 10 includes a screw head 12 and a threadedportion 15. The screw 10 has a recess 13 engageable with a screwdriver'sbit on a top surface 16 of the screw head 12. A shape of the recess 13is not particularly limited, such as a minus concave, a cross concave,and a star-shaped concave.

The recess 13 of this embodiment has a cross shape as illustrated inFIG. 2B. In this case, the recess 13 has four dents 13 a and one cone 13b. As illustrated in FIG. 2B, when the screw 10 is viewed from the top,each dent 13 a extends in the radial direction around a center 17 a thatis the center axis 17 of the screw 10 illustrated in FIG. 2A andcenterlines 13 a _(i) of these four dents 13 a spread at 90° intervalsaround the center 17 a. The cone 13 b is provided at the center of thescrew 10 using the center axis 17 as a center axis. R1 is a diameter ofa circle that passes an outermost part of the dents 13 a of the recess13. R2 is a diameter of a bottom surface of the cone 13 b (or aninternal diameter of the recess 13).

For the tray supply, the container 110 has a hole 112 into which thethreaded portion 15 of the screw 10 is inserted as illustrated in FIG.2A. A hole 112 is not threaded and the screw 10 is not fixed in the hole112. The screw 10 is sequentially supplied to the hole 112 along alongitudinal direction of the hole 112 and picked up from the hole 112by the screwdriver 120. The screw 10 is rotatable in the hole 112. Inthis embodiment, the screw 10 is mounted in the container 110 while aphase or direction of the recess 13 is not previously set. Since it isunnecessary to control the phase of the screw 10 beforehand, theinstallation operation of the screw becomes easier.

In this embodiment, the work W is a lower case (base) of a housing of acellular phone, and the screw fastener 100 screws an upper case (cover)of the housing that is a part of the cellular phone onto the lower case.In another embodiment, the work W is a hard disk drive (“HDD”), and thescrew fastener 100 screws a clamping ring as a part to a spindle hub ofthe HDD. The spindle hub is coupled with a spindle motor, mounted with amagnetic disk, and configured to rotate with the magnetic disk. Theclamping ring has a plurality of screw holes, and fixes onto the spindlehub with a constant pressure the magnetic disk that has been attachedaround the spindle hub.

The screwdriver 120 rotates a (screwdriver) bit 125, automaticallyfastens the screw 10, and includes a sleeve 121, a bit 125, a bitdriving system, a variety of types of detectors, and a suction system,as illustrated in FIG. 3.

FIG. 4A is an enlarged sectional view of the lower portion of the sleeve121 (a B part illustrated in FIG. 3). FIG. 4B is a bottom view of thesleeve 121 illustrated in FIG. 4A. FIG. 5A is an enlarged sectional viewof the lower portion of the sleeve 121 that has rotated clockwise by 45°from a rotational position illustrated in FIG. 4A. FIG. 5B is a bottomview of the sleeve 121 illustrated in FIG. 5A. FIG. 6A is a sectionalview of the lower portion of a conventional sleeve 2. FIG. 6B is abottom view of the sleeve 2 illustrated in FIG. 6A.

The sleeve 121 has a hollow, approximately cylindrical shape, a centerabsorption hole (hollow) 122 configured to absorb the top surface 16 ofthe screw 10, and a groove 123 at a rim, as illustrated in FIGS. 4B and5B. The absorption hole 122 accommodates the bit 125 and a part of ashaft 128. A material of the sleeve 121 is not limited. In thisembodiment, the sleeve 121 is made of resin, and the absorption hole 122and the groove 123 are formed by injection molding.

In prior art, a certain sleeve is fixed relative to a bit in fastening ascrew, and a screw head of the screw is inserted into the absorptionhole (or the absorption hole is larger than the top surface of thescrew), and the bit rotates and fastens the screw. However, in fasteningthe screw, a side surface of the screw head contacts the inner surfaceof the absorption hole of the sleeve and gets worn out, causing theabrasion powder. On the other hand, according to this embodiment, thesleeve 121 rotates with the bit 125, and the screw 10 and the sleeve 121rotate together. The absorption hole 122 is smaller than the top surface16 of the screws 10. As a result, no abrasion powder occurs.

As illustrated in FIGS. 4B and 5B, the adsorption hole 122 has asectional or bottom shape as well as a shape of the recess 13 of thescrew 10 and a shape of the tip 125 a of the bit 125. On the other hand,according to the prior art, the absorption hole 3 of the sleeve 2 has acylindrical shape as illustrated in FIGS. 6A and 6B. The bit 4 has thesame structure as that of the bit 125.

Thus, the absorption hole 122 of this embodiment has no cylindricalshape as in the prior art. The bit 125 may not have a cylindrical shapebecause it is rotated with the sleeve 121. More specifically, asillustrated in FIG. 4B, a bottom shape of the adsorption hole 122 hasfour concaves 122 a that retreat to the inside of a circle C illustratedby a dotted line which has an outer diameter R1 of the recess 13. Thisconcave 122 a can be used for a detector spot configured to detect anorientation or a phase of the recess 13 of the screw 10. It is necessarythat the detector spot corresponds to the recess 13 when the sleeve 121is located at a certain rotational position, and the detector spotshifts from the recess 13 when the sleeve 121 is located at anotherrotational position. Here, when the absorption hole 122 is viewed fromthe bottom, the center of cylindrical sleeve 121 or the center of bit125 accords with a center J corresponding to a center axis K of the bit125 or the sleeve 121. The circle C is a virtual circle having thecenter J as a center and passes the outermost diameter of the tip 125 aof the bit 125.

In this embodiment, there are four concaves 122 a corresponding to thecross shape. The cross-shaped adsorption hole 122 has four convexes 122b, and each convex 122 b has a centerline 122 b ₁ that extends in theradial direction from the center J. In other words, each convex 122 bextends along the centerline 122 b ₁. The centerline 122 b ₁ is a linewith respect to which each convex 122 b is in line symmetry. Asillustrated in FIGS. 4B and 5B, when the absorption hole 122 is viewedfrom the bottom, four centerlines 122 b ₁ spread around the center J at90° intervals.

As illustrated in FIGS. 7A, 7B, 8A and 8B, the groove 123 fluctuates thepressure in the absorption hole 122 according to the rotational positionof the sleeve 121 when the center axis 17 of the screw 10 is alignedwith the center axis K of the sleeve 121 (or the bit 125) and the bottomsurface 121 a of the sleeve 121 is located close to the top surface 16of the screw 10 in a noncontact manner. The groove 123 connects theadsorption hole 122 to and disconnects the absorption hole 122 from theexternal air according to the rotational position of the sleeve 121.

FIG. 7A is a sectional view of the lower portion of the sleeve 121 whenthe sleeve 121 is located close to the top surface 16 of the screw 10(at a distance of about 0.2 mm) FIG. 7B is a sectional view of FIG. 7Aviewed from an E-E direction. FIG. 8A is a sectional view of the lowerportion of the sleeve 121 located at a rotational position that hasrotated clockwise by 45° from FIG. 7A around the center J. FIG. 8B is asectional view of FIG. 8A viewed from an F-F direction. In FIGS. 7B and8B, the center axis K of the bit 125 or the sleeve 121 is aligned withthe center axis 17 of the screw 10 in the vertical direction.

The “noncontact” intends to exclude a situation in which dust anddeformations may occur at a contact spot when the sleeve 121 rotates(idles) while the bottom surface 121 a of the sleeve 121 contacts thetop surface 16 of the screw 10. The “close” is a location or distance atwhich the pressure fluctuation can be detected, and 0.2 mm in thisembodiment, although it is different according to a shape (such as across shape and a star shape) and a size (such as an outer diameter R1)of the recess 13 of the screw 10.

The groove 123 is separates from the absorption hole 122, and theabsorption hole 122 and the groove 123 are separated from a diaphragm121 c. When the groove 123 is connected to the absorption hole 122, aneffect of the pressure fluctuation reduces.

The groove 123 is formed in a bottom surface 121 a of the sleeve 121 asillustrated in FIGS. 4B and 5B. In addition, the groove 123 opens to airon the bottom surface 121 a and the cylindrical side surface 121 b ofthe sleeve 121. The groove 123 possesses a U-shaped outline when it isviewed from the bottom surface 121 a of the sleeve 121, and has a shapethat combines a quarter sphere and semi-cylinder with each other.

The groove 123 has a centerline 123 a that extends from the center J inthe radial direction, and an angle is 45° between the centerline 123 aand a centerline 122 b ₁ of a convex 122 b at both sides of the groove123 which are closest to the centerline 123 a. The centerline 123 a is aline with respect to which the groove 123 is in line symmetry. Thegroove 123 has an open end 123 b connected to the cylindrical sidesurface 121 b of the sleeve 121. A size of the open end 123 b is notlimited.

When the groove 123 is viewed from the bottom surface 121 a side of thesleeve 121, the groove 123 projects to the inside of the virtual circleC that passes the outermost diameter of the tip 125 a of the bit 125around the center J. In this embodiment, this projection is almost theabove quarter sphere (123 c of FIG. 8B). According to a rotationalposition of the sleeve 121, this projection 123 c may be connected to ordisconnected from the recess 13.

When the projection 123 c is disconnected from the recess 13 asillustrated in FIGS. 7A and 7B, the internal pressure of the absorptionhole 122 is maintained almost constant due to the absorption hole 122and the recess 13 although the bottom surface 121 a of the sleeve 121 isslightly spaced from the top surface 16 of the screw 10. On the otherhand, the internal pressure of the absorption hole 122 decreases whenthe projection 123 c is connected to the recess 13, as illustrated inFIGS. 8A and 8B, because the absorption 122 and the recess 13 and thegroove 123 are connected to each other and the absorption hole 122 isconnected to the groove 123 that opens to air via the recess 13.

Assume that n is the number of projections 126 of the tip 125 a of thebit 125 or the number of the convexes 122 b of the absorption hole 122(although n=4 in this embodiment). In this case, an angle may be set to360°/2n (or 45° in this embodiment) between the centerline 123 a of thegroove 123 and the centerline (not illustrated) of the projection 126 ofthe bit's tip 125 a closest to the groove 123 or the centerline 122 b ₁of the convex 122 b of the absorption hole 122 closest to the groove123. The projections 126 of the bit's tip 125 a or the convexes 122 b ofthe absorption hole 122 closest to the groove 123 are located on bothsides of the groove 123. Assume that the angle becomes equal to 360°/2nbetween the centerline 123 a of the groove 123 and the centerline 122 b₁ (126 a) at both sides of the groove 123. Then, after the groove 123 isaligned with the dent 13 a of the recess 13, the dent 13 a of the recess13 can be aligned with the projection 126 of the bit's tip 125 a even ifthe sleeve 121 is rotated by 360°/2n clockwise or counterclockwise. Ofcourse, once the rotational direction is determined, an angle betweentwo adjacent centerlines 122 b ₁ around the center J may be divided toan angle other than 360°/2n.

The groove 123 is disconnected from the recess 13 at the rotationalposition shown in FIGS. 7A and 7B. In addition, the groove 123 isconnected to the recess 13 when the sleeve 121 is located at arotational position illustrated in FIGS. 8A and 8B. The quarter sphere123 c of the groove 123 is arranged on the dent 13 a of the recess 13 inFIG. 8B. Thus, the groove 123 is connected to the recess 13 when thesleeve 121 is located at a certain rotational position and disconnectedfrom the recess 13 when the sleeve 121 is located at another rotationalposition.

FIGS. 7A and 7B illustrate that the phase of the dent 13 a of the recess13 accords with the phase of the convex 122 b of the sleeve 121 (or theprojection 126 of the tip 125 a of the bit 125), and the centerline 13 a₁ agrees with the centerline 122 b ₁. An arrow AC1 illustrated in FIG.7A represents an air channel. The air channel AC1 is formed in a gapbetween the bottom surface 121 a of the sleeve 121 and the top surface16 of the screw 10. Since the bottom surface 121 a of the sleeve 121 andthe top surface 16 of the screw 10 are arranged close to each other, theflow rate in the air channel AC1 is small.

FIGS. 8A and 8B illustrate that the phase of (the dent 13 a of) therecess 13 and (the convex 122 b of) the sleeve 121 shift from each otherby 45°, and one centerline 13 a ₁ among the four dents 13 a accords withthe centerline 123 a. An arrow AC2 illustrated in FIG. 8A represents anair channel. The air channel AC2 is formed by a gap between the bottomsurface 121 a of the sleeve 121 and the top surface 16 of the screw 10and the open end 123 b of the groove 123. Since a large amount ofexternal air flows in from the open end 123 b, the flow rate is large.The flow rate of the air channel AC1 and the flow rate of the airchannel AC2 are detected, and the groove 123 has a depth and a size ofthe open end 123 b so that a pressure difference between them can bedetected. This embodiment does not limit the depth of the groove 123 andthe size of the open end 123 b.

The bit 125 is a cylindrical member that includes the tip (bottom end)125 a and a proximal end (top end) 125 b.

The tip 125 a is engageable with the recess 13 of the screw 10, and hasa cross shape as illustrated in FIGS. 4B and 5B. This embodiment doesnot limit a shape of the bit's tip 125 a as long as the bit 125 canfasten the screw 10. The screw 10 can be fastened with the work W whenthe tip 125 a of the bit 125 is engaged with the recess 13 of the screw10 and rotated.

The tip 125 a of the bit 125 of this embodiment has four projections126. Each projection 126 is engageable with each dent 13 a of the recess13. When the sleeve 121 is viewed from the bottom surface side asillustrated in FIG. 4B, the tip 125 a is slightly smaller than therecess 13 of the screw 10 viewed from the top surface side asillustrated in FIG. 2B. Each projection 126 has the centerline 126 athat extends from the center J in the radial direction. In other words,each projection 126 extends along the centerline 126 a. The centerline126 a is a line with respect to which each projection 126 is in linesymmetry. Four centerlines 126 spread around the center J at 90°intervals when the tip 125 is viewed from the bottom surface, asillustrated in FIGS. 4B and 5B.

This embodiment makes the bit 125 of a magnetic material and the screw10 of metal. Thus, when the tip 125 a is engaged with the recess 13, thescrew 10 is fixed to the bit 125. As a result, the bit 125 is insertedinto and engaged with the recess 13 of the screw 10 in the container110, and when the bit 125 rises it can pick up the screw 10. However,since the absorption hole 122 adsorbs the top surface 16 of the screw10, the magnetic absorption is not necessarily required.

The proximal end 125 b is mechanically engaged with a bottom end 128 aof the shaft 128 of a bit driving system. Their engagement shapes arenot limited. As a result, the bit 125 and the shaft 128 rotate together.

The bit driving system is a mechanism configured to rotate and drive thebit 125, and includes the shaft 128, a gearbox 130, and a servo motor132.

The shaft 128 is a cylindrical member that includes the bottom end 128a, an engagement member 128 b, and a top end 128 c. The bottom end 128 ais engaged with the proximal end 125 b of the bit 125. A gear 131 e ofthe gearbox 130 of the bit driving system is fixed around the engagementmember 128 b. As a result, the shaft 128 rotates with the gear 131 e.The top end 128 c of the shaft 128 has a notch 128 c ₁ as illustrated inFIG. 9. Here, FIG. 9 is an enlarged side view and sectional view of theA part in FIG. 3. It is optional to provide the bit 125 and the shaft128 as separate members, and the bit 125 and the shaft 128 may beintegrated into one body.

The servo motor 132 has a motor shaft 133, and is supplied with thepower via a cable (not shown). A gear 131 a of the gearbox 130 isprovided around the motor shaft 133. Therefore, the motor shaft 133 andthe gear 131 a rotate together. The motor shaft 133 projects with thegear 131 a from a hole of a lid 131 i of the gearbox 130 to the insideof the gearbox 130.

A variety of detectors include a rotational position detector 140, arotational position detector (encoder) 144, and a vacuum monitoringdetector 146.

The gearbox 130 transmits the power (torque) of the motor 132 to theshaft 128. A case 131 f of the gearbox 130 is fixed onto the sleeve 121,and the case 131 f is covered by the lid 131 i. The gearbox 130 includesa gear row (gears 131 a to 131 e). The gear 131 a is fixed around themotor shaft 133 of the motor 132 and rotates with the motor shaft 133.The gear 131 b is fixed around the axis 131 g, and engaged with the gear131 a. The axis 131 g is rotatably held by the case 131 f. The gear 131c is fixed around the axis 131 g and engaged with the gear 131 d. Thegear 131 d is fixed around the axis 131 h and engaged with the gear 131e. The axis 131 h is rotatably held by the case 131 f. As a result, therotational force of the motor 132 is transmitted to the shaft 128.

The rotational position detector 140 is configured to detect that thebit 125 engaged with the shaft 128 is located at a rotational position(origin position) by detecting a rotational position of the shaft 128.The rotational position detector 140 is an optical sensor and includes,as illustrated in FIG. 9, a light emitter 141 a, a light receiver 141 b,and a frame 142 that supports the light emitter 141 a and the lightreceiver 141 b. However, a type of the sensor 140 is not limited to thetransmission type optical sensor.

Light L that travels from the light emitter 141 a to the light receiver141 b can be detected only when a notch 128 c ₁ of the top end 128 c ofthe shaft 128 is located at a position illustrated in FIG. 9. Adetection result by the light receiver 141 b is transmitted to thecontroller 170. The frame 142 is fixed onto a support plate 134 having aplate shape, and the support plate 134 is fixed onto one end of anL-shaped support plate 136 by the screws 135. The other end of thesupport plate 136 is fixed onto the lid 131 i of the gearbox 130 withthe screw 137. As a result, the frame 142 is fixed onto the gearbox 130.

The notch 128 c ₁ is made by cutting an arc sectional shape from theshaft 128 in the longitudinal direction of shaft 128. The vertical endsurface of the notch 128 c _(i) decenters from the vertical center axisof the shaft 128. When the vertical end surface of the notch 128 c ₁contains the vertical central axis of the shaft 128, the detector 140similarly detects it even when the shaft 128 is rotated by 160°, and therotational position of the shaft 128 cannot be uniquely detected. Ofcourse, since the bit 125 is symmetrical even if it rotates by 180°, theend surface may be formed at the center. The notch 128 c ₁ detected bythe detector 140 is not limited to a shape illustrated in FIG. 9. Forinstance, it may be formed as a concave (groove) or a projection.

As described above, the screw 10 is accommodated in the container 110while its phase and orientation are not aligned with constantdirections. Therefore, even if the bit 125 is positioned at the originposition by the rotational position detector 140, it is not alwaysinserted into and engaged with the recess 13 with no rotation. In otherwords, the tip 125 a of the bit 125 is not aligned with the recess 13 ofthe screw 10 only by positioning the bit 125 to the origin position.

The rotational position detector 144 is an encoder configured to detecta rotational angle of the motor 132. The rotational position detector144 is provided to the motor shaft 133, and is a rotary encoderconfigured to detect the rotational position of motor shaft 133, and isconnected to the controller 170. The rotational position detector 144can be used to detect the rotational position of the bit 125, and inthis case the controller 170 may use only one of the rotational positiondetectors 140 and 144. This embodiment uses the rotational positiondetector 140 so as to return the bit 125 to the origin position, anduses the rotational position detector 144 for an alignment between thetip 125 a of the bit 125 and the recess 13 of the screw 10 based on thedetection result of the vacuum monitoring detector 146.

The rotary encoder when it is an absolute type can detect an absoluteposition as well as the rotational position detector 140. Thus, in thiscase, the rotational position detector 144 sets the rotational position(rotational angle) of the motor shaft 133 to the origin when the bit 125is located at the origin position and detects it. On the other hand, therotary encoder when it is an increment type can calculate a rotationaldirection and a rotational amount based on a phase shift between twopulses. Since the rotational amount in this case is a rotational amountof the motor shaft 133, the rotational amount of motor shaft 133 ismultiplied by a gear ratio so as to convert it into the rotationalamount of bit 125. After the rotational amount is calculated necessaryfor the bit 125 to return to the origin position, it may be convertedinto a rotational amount of the motor shaft 133.

The suction system (vacuum drawing unit) sucks the inside of theabsorption hole 122 of the sleeve 121, decreases the internal pressure,and provides the bottom of the sleeve 121 to attract the screw 10. Thesuction system includes a suction plug 150, a tube 152 attached to thesuction plug 150, and a vacuum pump 154. The suction plug 150 includes athreaded portion 151 a connected to the absorption hole 122 of thesleeve 121, and a connector 151 b connected to the tube 152. One end ofthe tube 152 is connected to the connector 151 b of the suction plug150, the other end of the tube 152 is connected to the vacuum pump 154,and an intermediate portion of the tube 152 is connected to the vacuummonitoring detector 146. The tube 152 includes not only the metallicpiping but also elastic members such as a hose and a tube. A well-knownstructure is applicable to the vacuum pump 154.

The vacuum monitoring detector 146 is a pressure gauge or a flow meterconfigured to detect the internal pressure of the tube 152 (or the holeabsorption hole 122 of the sleeve 121), and informs the detection resultto the controller 170.

The movement unit 160 serves to three-dimensionally move the screwdriver120 between the container 110 and the work W, and includes an X-axisrobot 162, a Y-axis robot 164, and a Z-axis robot 166. The X-axis robot162 moves the screwdriver 120 in the lateral direction illustrated inFIG. 1. The Y-axis robot 164 moves the screwdriver 120 in thelongitudinal direction illustrated in FIG. 1. The Z-axis robot 166 movesthe screwdriver 120 in a direction perpendicular to the paper plane ofFIG. 1. These robots can apply a well-known structure in the art, and adetailed description thereof will be omitted.

The control system includes the controller 170. The controller 170controls a rotation of the servo motor 132 of the screwdriver 120 and amovement of the screwdriver 120 by the movement unit 160 in picking upthe screw 10, in mounting the screw 10, and in fastening the screw 10.The controller 170 includes a processor such as a MPU, and a memory (notillustrated) such as a RAM, and ROM. The controller 170 controlsoperations of the screwdriver 100 and the movement unit 160 so that thescrew 10 can be picked up from the container 110 for storing the screws10, and the part is fixed onto the work W by the screw 10.

A description will now be given of the operation of the screw fastener100 (controller 170) with reference to the flowchart illustrated inFIGS. 10 to 12.

Firstly, an initialization is performed (step 1100).

In the initialization, as illustrated in FIG. 11, the teaching of shapesof the sleeve 121 and the bit 125 is performed (step 1102). In the step1102, for example, the controller 170 stores information that thecenterlines 122 b ₁ of the convex 122 b of the sleeve 121 and thecenterlines 126 a of the projection 126 of the tip 125 a of the bitspread at 90° (more specifically 360°/2n) intervals, and the centerline123 a of the groove 123 is arranged at an angle of 45° (such as 360°/2n)with respect to two adjacent centerlines 122 b ₁ or 126 a.

Next, the teaching of the arrangement of the screw(s) 10 is performed(step 1104). In the step 1104, for instance, the controller 170 storesinformation of the center coordinates of the holes 112 for one or morescrews 10 in the container 110. Thereby, the controller 170 calculatesand stores a movement amount of each robot of the movement unit 160 inaligning the center axis K of the sleeve 121 or bit 125 with the centeraxis 17 of each screw 10.

Next, the screw 10 is picked up by the movement unit 160 (step 1200).Referring now to FIG. 12, a detailed description will be given of thepickup operation of the step 1200.

Initially, the controller 170 determines whether the container 110configured to house the screw 10 is placed on a worktable (notillustrated) (step 1202). This determination can use a detection resultof a detector and a camera (not illustrated) provided to the worktable(not illustrated). In addition, at the same time, the controller 170determines whether there is a screw in the container 110. While thisembodiment accommodates only one screw 10 in the container 110, aplurality of screws 10 may be simultaneously picked up and attached tothe work W in another embodiment. For instance, when six screws arepicked up at the same time using six screwdrivers 120, the controller170 determines whether a predetermined number of (or 6) screws 10 arehoused in the container 110. This determination is made by the detectoror the camera provided to the container 110 which is configured todetect whether the screw hole of the container 110 is closed. Thecontroller 170 waits for picking up until these conditions aresatisfied, and provides an error indication if necessary. In the step1202, the direction of the recess 13 of the screw 10 is arbitrary, andthe controller 170 does not recognize that direction.

Next, the bit 125 is returned to the origin position (step 1204). In thestep 1204, the controller 170 of this embodiment acquires the detectionresult of rotational position detector 140, drives the servo motor 132based on the detection result, rotates the shaft 128 and the bit 125. Inthe step 1204, when it is determined that the bit 125 is not at theorigin position, the controller 170 rotates the bit 125 via the motor132 until the light receiver 141 b of detector 140 detects the light Lor the bit 125 is moved to the origin position. Thereby, the bit 125 ispositioned in the state illustrated in FIG. 9.

Next, the screwdriver 120 is descended to a search position until thebottom surface 121 a of the sleeve 121 is located close to the topsurface 16 of the screw 10 in a noncontact manner (step 1206). At thesearch position, a distance between the bottom surface 121 a of thesleeve 121 and the top surface 16 of the screw 10 is, for instance, asillustrated in FIGS. 7A and 8A. In the step 1206, the controller 170drops the screwdriver 120 via the Z-axis robot 166 of the movement unit160.

Next, the sleeve 121 and the bit 125 are rotated through the servo motor132 (search) (step 1208). A minimum rotational angle is 360°/n. Amaximum rotational angle is 360°. For instance, assume that as a resultof the step 1206, the groove 123 is located at a position illustrated inFIG. 7B (although an angle between the centerline 123 a of the groove123 and the adjoining centerline 122 b ₁ (and 126 a) need not be 45°).When the sleeve 121 and the bit 125 are rotated around the center Jclockwise, the centerline 123 a of the groove 123 reaches the positioncorresponding to the centerline 13 a ₁ of the right dent 13 a asillustrated in FIG. 8B. At this time, since the flow rate of the airchannel AC2 is large as illustrated in FIG. 8A, the pressure dropbecomes a peak. This peak of the pressure drop appears every 90° whenthe rotational angle of the step 1208 is 360°.

While this embodiment provides one groove 123, the number of grooves 123is not limited. For instance, as illustrated in FIGS. 14 and 15, fourgrooves 123 may be provided to the sleeve 121. Here, FIG. 14A is asectional view of the lower portion of the sleeve 121 when the sleeve121 and screw 10 are close to each other (at a distance of about 0.2 mm)FIG. 14B is a sectional view of FIG. 14A viewed in an E1-E1 direction.FIG. 14B is a variation of FIG. 7B, and provides four grooves 123 on thebottom surface 121 a of the sleeve 121. FIG. 15A is a sectional view ofthe lower portion of the sleeve 121 located at a position that isrotated clockwise by 45° from FIG. 14A. FIG. 15B is a sectional view ofFIG. 15A viewed from an F1-F1 direction. In FIG. 15B, the center axis Kof the sleeve 121 (bit 125) is aligned with the center axis 17 of thescrew 10 in the vertical direction.

FIGS. 14B and 15B illustrate four grooves 123 and FIG. 7B and 8Billustrate one groove 123 but each groove 123 is identically structured.The groove 123 has the centerline 123 a that extends from the center Jin the radial direction, and an angle is 45° between the centerline 123a and the centerline 122 b ₁ of the convex 122 b that is closest to thecenterline 123 a. The centerlines 123 a are distributed at 90° intervalswith respect to the center axis K. When each groove 123 is viewed fromthe bottom surface 121 a, each groove 123 projects inside of the virtualcircle C that passes the outermost diameter of the tip 125 a of the bit125 around the center J. This projection may be connected to ordisconnected from the recess 13 according to a rotational position ofthe sleeve 121.

When each projection is disconnected from the recess 13 as illustratedin FIGS. 14A and 14B, the internal pressure of the absorption hole 122is maintained constant to some extent by the absorption hole 122 and therecess 13 although the bottom surface 121 a of the sleeve 121 isslightly spaced from the top surface 16 of the screw 10. On the otherhand, when each projection is connected to the recess 13 as illustratedin FIG. 15A and 15B, the internal pressure of the absorption hole 122lowers since the absorption hole 122, the recess 13, and the groove 123are connected with one another and the absorption hole 122 is connectedto the groove 123 that is open to air via the recess 13.

FIGS. 14A and 14B illustrate that the phase of the dent 13 a of eachrecess 13 accords with the phase of each convex 122 b of the sleeve 121(or each projection 126 of the tip 125 a of the bit 125), and thecenterline 13 a ₁ accords with the centerline 122 b ₁ (or 125 a ₁). Anarrow AC3 illustrated in FIG. 14A represents an air channel. The airchannel AC3 is formed in a gap between the bottom surface 121 a of thesleeve 121 and the top surface 16 of the screw 10. The flow rate thatflows in the air channel AC3 is small as well as the air channel AC1.

FIGS. 15A and 15B illustrate that the phase of (the dent 13 a of) therecess 13 shifts by 45° from the phase (of the convex 122 b) of thesleeve 121, and the centerlines 13 a ₁ of four dents 13 a correspond tothe centerlines 123 a of the four grooves 123. An arrow AC4 illustratedin FIG. 15A represents an air channel. The air channel AC4 contains agap between the bottom surface 121 a of the sleeve 121 and the topsurface 16 of the screw 10, and open ends 123 b of the four grooves 123,and the flow rate is large since the external air flows in from the openends 123 b. The flow rate of the air channel AC3 and the flow rate ofthe air channel AC4 are the pressure to be detected.

A flow rate difference between the air channel AC3 and the air channelAC4 is larger than a flow rate difference between the air channel AC1and the air channel AC2. Since the peak value of the pressure dropbecomes approximately quadruple and the S/N ratio improves, thedetection accuracy of the peak position of the pressure drop improves.In addition, the influence of the shape error on the peak positionbecomes smaller in producing the groove 123 and the recess 13 becausethe flow rates of the four air channels AC4 are summed up using the fourgrooves 123 than use of only one groove (due to the averaging effect).

Turning back to FIG. 12 again, the controller 170 next obtainsinformation of the rotational position of the sleeve 121 (bit 125) whenthe centerline 123 a of the groove 123 accords with the centerline 13 a₁ of the dent 13 a of the recess 13 of the screw 10 based on a detectionresult of the vacuum monitoring detector 146 and a detection result ofthe rotational position detector 144 (step 1210). When the controller170 rotates the bit 125 by 360°/n in the step 1208, the controller 170obtains information of the peak position of the pressure drop (or therotational angle of the sleeve 121 (bit 125) illustrated in FIG. 8B).The controller 170 selects information of one of four peak positions ofthe pressure drop when the controller 170 rotates the bit 125 by 360° inthe step 1208. In addition, the controller 170 obtains a correctionvalue from the teaching information in the step 1102 (step 1210). Thecorrection amount is an angular difference between the centerline 123 aof the groove 123 and the centerline 126 a of the bit 125, and thus 45°in this embodiment. As a result, the controller 170 recognizes that thephase of the tip 125 a of the bit 125 accords with the phase of therecess 13 of the screw 10 when the rotational position of the bit 125illustrated in FIG. 8B is shifted to the position by 45°, and obtainsinformation (of the alignment angle) of the rotational angle of thesleeve 121 (bit 125).

Next, the controller 170 rotates the sleeve 121 (bit 125) to theposition of the alignment angle acquired in the step 1210 (step 1216).As a result, the phase of the tip 125 a of the bit 125 accords with thephase of the recess 13 of the screw 10.

Next, the controller 170 descends the screwdriver 120 (step 1218),engages the tip 125 a of the bit 125 with the recess 13 of the screw 10,and absorbs the screw 10 as illustrated in FIG. 13 (step 1220). Here,FIG. 13 is a sectional view of an engagement between the tip 125 a ofthe bit 125 and the recess 13 of the screw 10.

Due to a highly precise alignment, the tip 125 a of the bit 125 can beengaged with the recess 13 of the screw 10 with no rotation. As aresult, deformations and damages of the tip 125 a of the bit 125 and/orthe recess 13 of the screw 10, and generations of the abrasion powdercan be prevented. Thus, a variety of problems can be solved, includingthe pollution and the electric short circuit caused by the abrasionpowder, a generation of a torque transmission loss, and a short life ofthe bit 125, and a decrease of the operating rate due to the exchange ofthe bit 125.

Then, the controller 170 ascends the screwdriver 120 that absorbs thescrew 10 via the Z-axis robot 166 of the movement unit 160, andcompletes picking up of the screw (step 1222). The bit 125 can use themagnetism to pick up the engaged screw 10, as described above.

Turning back to FIG. 10 again, the controller 170 moves the screwdriver120 to a position above the screw holes of the work W and the part viathe X-axis robot 162 and the Y-axis robot 164 of the movement unit 160(step 1300). A coordinate of the center position of the screw hole ispreviously input to the movement unit 160. Next, the controller 170descends the screwdriver 120 via the Z-axis robot 166 of the movementunit 160, and brings the screw 10 into contact with the screw hole (step1400). Next, the controller 170 fastens the screw 10 into the screw holevia the motor 132 (step 1500).

The fastening in the step 1500 means permanent fastening, butprovisional fastening may be performed beforehand if necessary. Theprovisional fastening means fastening of a predetermined amount withoutseating of the screw 10. The permanent fastening means completefastening of the screw for fixation. However, when there are a largenumber of screws, it is likely that fastening of the screw is difficultor unable because the screw hole of the part shifts from the screw holeof the work. Accordingly, the provisional fastening in which the screwis floated from the seating position is needed so that the attachmentposition of the part can be adjusted. In this case, all screws arepermanently fastened after the provisional fastening is completed. Thepermanent fastening is completed through seating and torquing-up. Theseating means a contact between the seat of the screw and the surfacearound the screw hole, and the torque-up means fastening with apredetermined torque and fixing of the seated screw.

Next, the controller 170 determines whether the screws 10 have beenfastened into all screw holes (step 1600). When the controller 170determines that the screws 10 have been fastened into all screw holes,the controller 170 completes the screw fastening process and returns tothe step 1200 when determining that the screws 10 have not beenfastened.

This embodiment detects the origin position of the bit 125 using thedetection result of the rotational position detector 140, but anotherembodiment detects it using the detection result of the rotationalposition detector 144, as described above.

While this embodiment provides the groove 123 to the bottom surface 121a of the sleeve 121, the pressure fluctuation unit is not limited tothis embodiment. For instance, as illustrated in FIG. 16, a groove 18may be provided in a screw 10A. The screw 10A is different from thescrew 10 in that the screw 10A has the groove 18. In this case, it isunnecessary to provide the groove 123 on the bottom surface 121 a of thesleeve 121. The groove 18 fluctuates the pressure in the absorption holeaccording to the rotational position of the sleeve when the bottomsurface of the sleeve is located close to the top surface 16A of thescrew 10A in a noncontact manner. Here, FIG. 16 is an enlarged plan viewof the screw 10A.

The groove 18 is separated from the recess 13, and the recess 13 and thegroove 18 are separated by the diaphragm 19. The groove 18 is opened toair on the top surface 16A of the screw 10A and a side surface 14 of thescrew 10A. The groove 18 has a U-shaped contour when viewed from the topsurface side of the screw 10A, and has a shape that combines a quartersphere with a cylinder. The groove 18 has a centerline 18 a that extendsfrom the center J in the radial direction, and an angle is 45° betweenthe centerline 18 a and the centerline 13 a 1 of the dent 13 a that isclosest to the centerline 18 a. The centerline 18 a means a line withrespect to which the groove 18 is in line symmetry. The groove 18 has anopen end 18 b connected to the side surface 14 of the screw head. Thesize of the open end 18 b is not limited.

The groove 18 projects inside of a virtual circle C1 that has an outerdiameter R1 of the recess 13 around the center 17 a. In this embodiment,this projection is the above quarter sphere. This projection isconnected to or disconnected from the convex of the sleeve according tothe rotational position of the sleeve. Thus, the groove 18 has the samefunction as that of the groove 123.

According to the suction system of this embodiment, when the bit 125 isattempted to rotate with the sleeve 121, the suction plug 150 is rotatedsince the suction plug 150 is fixed onto the sleeve 121. However, it isdifficult to rotate the attraction system since the vacuum drawing tube152 is attached to the suction plug 150. Accordingly, the lower portionof the screwdriver 120 may be modified to the structure illustrated inFIG. 17.

In FIG. 17, a work W is a lower case (base) of a housing of a cellularphone, and the screw fastener 100 screws an upper case (cover) P of thehousing that is a part of the cellular phone onto the lower case. Theupper case P has a plurality of bores Pa and the upper case P is screwedonto the lower case by fastening the screws 10 in the bores Pa.

FIG. 17 is a partially enlarged sectional view of the lower portion ofthe screwdriver 120A. FIG. 18 is an exploded perspective view of theessential components illustrated in FIG. 17. Referring to FIGS. 17 and18, the lower portion of the screwdriver 120A of this embodimentincludes sleeves 180A, 180B, a sleeve holder 190, a cover 200, a bit210, and a suction plug 150. The sleeve 180B, the sleeve holder 190, thecover 200, and the bit 210 are aligned with the same axis.

The sleeve 180A is a hollow, thin cylindrical member, and includes acentral perforation hole 181 a that extends in the Z-axis direction, aside perforation hole 181 b that extends in the radial direction, and anannular bottom surface 181 c. The Z-axis direction is a direction thataccords with a longitudinal direction of the bit 210. Since the sleeve180A and the sleeve 180B are not integrally formed, the sleeve 180A doesnot rotate even when the sleeve 180B is rotated with the bit 210. Thesleeve 180A and the suction plug 150 are formed as one unit.

The sleeve 180A accommodates a part of a base 213 of the bit 210 in thecentral perforation hole 181 a. The suction plug 150 is installed in theside perforation hole 181 b at the lower portion of the sleeve 180A. Thebottom surface 181 c is placed on a flange 192 of the sleeve holder 190.

The sleeve 180B includes an engagement member 182, a central member 183,a flange 184, and a tip 185, and is accommodated in the sleeve holder190 so that the sleeve 180B can move relative to the sleeve holder 190.In other words, the sleeve 180B can move in the Z-axis direction androtate around the Z axis in the sleeve holder 190.

The engagement member 182 has a hollow, cylindrical shape, and islocated at the uppermost position in the sleeve 180B. The engagementmember 182 includes a top end surface 182 a orthogonal to the Z axis,and a pair of grooves 182 b having the same shape. The top end surface182 a contacts a compression spring 215 directly or via a washer 217. Aprojection 216 is inserted into each groove 182 b, and each groove 182 bextends in the Z-axis direction. A direction in which the groove 182 bextends is not limited, but if the groove 182 b extends in the Z-axisdirection, both clockwise and counterclockwise rotations of the bit 210are likely to transmit to the sleeve 180B. The number of grooves 182 band the interval between the grooves 182 b correspond to the number ofprojections 216 and the interval between the projections 216. The widthof groove 182 b is slightly wider than a width (diameter) of theprojection 216. As the bit 210 rotates, the projection 216 contacts andcompresses the contour surface 182 c that defines the groove 182 b. As aresult, the sleeve 180B rotates with the bit 210.

The central member 183 contacts a side surface 193 a of a secondcylinder 193 of the sleeve holder 190 via an outer side surface 183 a.The outer diameter of the central member 183 is approximately equal tothe inner diameter of the second cylinder 193 of the sleeve holder 190and engaged with the second cylinder 193 with a predetermined clearance.The outer diameter of the central member 183 is larger than the innerdiameter of a first cylinder 191 of the sleeve holder 190. Thus, whileFIG. 17 illustrates that the sleeve 180B can be inserted through thefirst cylinder 191 side but actually it is inserted into the sleeveholder 190 from the bottom side (second cylinder 193 side) of the sleeveholder 190.

The flange 184 is pressed against an inner surface 201 a of a bottom 201(near a perforation hole 201 b) of the cover 200 by the compressionspring 215. The pressure is set slightly larger than the force movingthe sleeve 180B in the Z2 direction in the decompression time of theabsorption hole 186. Thereby, a Z-axis position of the sleeve 180B isdetermined

The tip 185 has an absorption hole 186 for the vacuum absorption of apart of the top surface 16 of the screw 10. The adsorption hole 186 is acentral perforation hole of the sleeve 180B, and has two kinds ofcylinders having different diameters. However, as described above, thebase 213 and the operation part 214 may have the same diameter and inthat case the absorption hole 186 has a cylindrical shape having thesame diameter. The absorption hole 186 has a first hole 186 a that canaccommodate the base 213, and a second hole 186 b that can accommodatethe operation part 214 but cannot accommodate the base 213. In thisembodiment, the outer shape of the tip 185 and the diameter of thesecond hole 186 b are smaller than the diameter of the screw head 12 ofthe screw 10 engageable with the bit 210.

The sleeve 180B is made of anti-static resin. Resin provides a smoothrotation of the sleeve 180 relative to the sleeve holder 190 and ananti-static material prevents a damage of the sleeve 180B due toelectric charges.

The sleeve holder 190 has a convex section shape, and is made ofstainless steel in this embodiment. The sleeve holder 190 includes afirst cylinder 191, a flange 192, a second cylinder 193, and a centralperforation hole 194.

The first cylinder 191 is inserted into the sleeve 180A, and has anouter diameter that is approximately equal to an internal diameter ofthe sleeve 180A, and contacts the inner surface of the sleeve 180A. Thefirst cylinder 191 has a hollow cylindrical shape, and a sideperforation hole 191 b on the side surface 191 a which extends in theradial direction, and the threaded portion 151 a of the suction plug 150is attached to the side perforation hole 191 b through the sideperforation hole 181 b of the sleeve 180A.

The flange 192 contacts and positions the bottom surface 181 c of thesleeve 180A.

The diameter of the second cylinder 193 is larger than that of the firstcylinder 191. The second cylinder 193 contacts the inner surface 202 aof the side surface 202 of the cover 200, and the cover 200 is inserted.The diameter of the second cylinder 193 is approximately equal to thediameter of the central member 183 of the sleeve 180B.

The second cylinder 193 has a hollow cylindrical shape, and has a sideperforation hole 193 b that extends in the radial direction at an upperportion of the side surface 193 a. The side perforation hole 193 b is ascrew hole aligned with the side perforation hole 202 b of the sidesurface 202 of the cover 200. The side perforation hole 202 b is an ovalthat is long in the Z-axis direction. A threaded portion 204 a of thescrew 204 is inserted into the side perforation holes 193 b and 202 b,and the cover 200 is fixed onto the sleeve holder 190. The secondcylinder 193 accommodates the sleeve 180B so that the sleeve 180B can bemoved in the Z-axis direction and rotated around the Z axis.

The central perforation hole 194 has a convex section shape, and isconnected to the absorption hole 186 of the sleeve 180B. The centralperforation hole 194 includes a first hole 194 a in the first cylinder191, and a second hole 194 b in the second cylinder 193. The first hole194 a and the second hole 194 b have cylindrical shapes, and thediameter of the second hole 194 b is larger than the diameter of thefirst hole 194 a. The first hole 194 a accommodates the bit 210 and thecompression spring 215. The second hole 194 b accommodates the bit 210,the compression spring 215, the washer 217, and the sleeve 180B.

The cover 200 has a hollow, cylindrical shape that has an open topsurface, and includes a bottom 201 and a side surface 202.

The bottom 201 contacts the flange 184 of the sleeve 180B in theinternal surface 201 a. A central perforation hole 201 b is formed atthe center of the bottom 201. Since an outer side surface 183 a of thecentral member 183 of the sleeve 180B and the side surface 193 a of thesecond cylinder 193 have approximately the same diameter, the inflow ofthe air at the boundary is reduced so as to maintain the decompressionenvironment.

The side perforation hole 202 b is formed in the radial direction at theupper portion of the side surface 202. The threaded portion 204 a of thescrew 204 is inserted into the side perforation holes 193 b and 202 a,and thereby the cover 200 is fixed onto the sleeve holder 190 in theZ-axis direction. The side perforation hole 202 b is formed as an ovalthat is long in the Z-axis direction. Thereby, the Z-axis position ofthe sleeve holder 190 of the cover 200 is adjustable. The oval, sideperforation hole 202 b and the screw 204 are used to adjust the Z-axisposition of the cover 200 relative to the sleeve holder 190, and forms afixation unit configured to fix the cover 200 and the sleeve holder 190.An adjustment of the Z-axis position of the cover 200 relative to thesleeve holder 190 means that the Z-axis position of the sleeve 180B isadjustable in FIG. 17.

The bit 210 is a rod member that extends in the Z-axis direction, andincludes an end 211, a neck 212, a base 213, and an operation part 214.

The end 211 has a semicircular engagement part 211 a engageable with asemicircular end (not illustrated) of the shaft 128 on the top, and anengagement of them forms a cylinder. Thereby, a driving force of adriving system is transmitted as a rotational driving power around the Zaxis to the bit 210. The shaft 128 and the bit 210 may be integratedwith each other.

The neck 212 is a narrow part formed between the end 211 and the base213, and binds the bit 210 and releases the bit 210 in the Z-axisdirection by inserting a steel ball (engagement member) (notillustrated) into the neck 212 and ejecting the steel ball from the neck212.

The base 213 is coupled with the bottom of the end 211 via the neck 212.The compression spring 215 is provided around the base 213, and thelower portion of the side surface 213 a has a pair of projections 216.

The compression spring 215 is latched by an engagement member (notillustrated) fixed on the sleeve 180A at one end 215 a, and by the topend surface 182 a of the sleeve 180B at the other end 215 b via thewasher 217. It is optional to provide the washer 217. Thereby, thecompression spring 215 forces the sleeve 180B in the Z1 direction. Thecompression spring 215 presses the sleeve 180B against the internalsurface 201 a of the bottom 201 of the cover 200. Thereby, at thedecompression time of the absorption hole 186, the position can bemaintained.

A pair of projections 216 is provided to the side surface 213 a of thebase 213. Each projection 216 is engaged with the groove 182 b of thesleeve 180B, and transmits to the sleeve 180B the driving force of themotor 132 which has been transmitted to the end 211. This embodimentmakes perforation holes in the side surface 213 a of the base 213 in adirection perpendicular to the Z-axis direction, and forms theprojections 216 by inserting a pin into the perforation holes. However,the structure of the projections 216 is not limited to this embodiment.

The operation part 214 has a tip 214 a at the top which is engageablewith the recess 13 of the screw 10. A shape of the tip 214 a correspondsto the shape of the recess 13. When the tip 214 a is engaged with therecess 13 of the screw 10 and rotates together, the bit 210 can fastenthe screw 10 in the work W using the driving force applied by the motor132.

The screwdriver 120A inserts the screw 10 into the bore Pa, asillustrated in FIG. 19A in the step 1400 illustrated in FIG. 10.Subsequently, as illustrated in FIG. 19B, the screw 10 is fastened intothe screw hole in the bore Pa via the motor 132 (step 1500). In the step1500, the bit 210 and sleeve 180A rotate with the screw 10, and thesleeve 180B, the sleeve holder 190, and the cover 200 are maintainedstationary. Since suction plug 150 stops, a structure in which the tube152 that is required to stand still may be used.

Referring now to FIGS. 20 to 23, a variation of the flowchartillustrated in FIG. 12 will be described. FIG. 20 is a variation of theflowchart illustrated in FIG. 11, and those reference numerals in FIG.20 which are the same reference numerals in FIG. 11 will be designatedby the same reference numerals, and a description thereof will beomitted. FIG. 20 is different from the flowchart illustrated in FIG. 12in that FIG. 20 has the step 1106. FIG. 21 is a variation of theflowchart illustrated in FIG. 12, and those reference numerals in FIG.21 which are the same reference numerals in FIG. 12 will be designatedby the same reference numerals, and a description thereof will beomitted. FIG. 21 is different from the flowchart illustrated in FIG. 12in that FIG. 21 has the steps 1212 and 1214. FIG. 22 is a plane viewthat illustrates a positional shift between the groove 123 and the dent13 a of the recess 13 when there is a positional shift between thecenter axis 17 of the recess 13 of the screw 10 and the center axis K ofthe sleeve 121 (bit 125). FIG. 23 is a graph illustrating a relationshipbetween a rotational angle of the sleeve 121 (bit 125) and an output ofthe vacuum monitoring detector 146.

Assume that the center axis 17 of the recess 13 of the screw 10 (center17 a) shifts from the center axis K of the sleeve 121 (bit 125) (centerJ) as illustrated in FIG. 22, and the recess 13 has a plurality of dents13 aA to 13 aD. For simple description, the center 17 a shifts from thecenter J in the lateral direction (horizontal direction) in FIG. 22, andQ denotes a positional shift. In addition, the dents 13 aA to 13 aD arearranged clockwise illustrated in FIG. 22. In FIG. 22, the groove 123rotates with the sleeve 121, and the centerline 123 a of the groove 123becomes parallel to the centerline 13 a 1 of each dent 13 a for each90°. While FIG. 22 illustrates four grooves 123, this figure actuallyillustrates that only one groove 123 rotates by 360°.

An overlap area 123 cA between the groove 123 and the dent 13 aA whenthe centerline 123 a of the groove 123 accords with the centerline 13aA1 of the dent 13 aA is smaller than an overlap area 123 cC between thegroove 123 and the dent 13 aC when the centerline 123 a of the groove123 accords with the centerline 13 aC1 of the dent 13 aC. An overlaparea 123 cB between the groove 123 and the dent 13 aB when thecenterline 123 a of the groove 123 accords with the centerline 13 aB1 ofthe dent 13 aB is equal to an overlap area 123 cD between the groove 123and the dent 13 aD when the centerline 123 a of the groove 123 accordswith the centerline 13 aD1 of the dent 13 aD.

Initially, it is premised that the controller 170 stores the teaching ofa relationship between a positional shift amount and the pressure or theflow rate detected by the vacuum monitoring detector 146 when anaccordance between the center 17 and the center J (or the ideal statewhen the positional shift amount is 0) destroys (step 1106 in FIG. 20).Thereby, the controller 170 can obtain the detection result of thevacuum monitoring detector 146 and can convert it into a positionalshift.

FIG. 23 illustrates four peaks of the pressure drop detected by thevacuum monitoring detector 146 corresponding to the overlap areas 123 cAto 123 cD. The pressure drop corresponding to the overlap areas 123 cBand 123 cD have the same peak values. The pressure drop corresponding tothe overlap area 123 cA has the lowest peak value, and the pressure dropcorresponding to the overlap area 123 cD has the highest peak value.

When the controller 170 obtains information illustrated in FIG. 23, thecontroller 170 recognizes that there is no positional shift between thecenter 17 a and the center J in the longitudinal direction(perpendicular direction), since the pressure drops corresponding to theoverlap areas 123 cB and 123 cD have equal peak values (or from thedetection result of the vacuum monitoring detector 146 and the teachingin step 1106) (step 1212 in FIG. 21). In addition, the controller 170recognizes that there is a positional shift amount Q due to a differenceE between the peak value of the pressure drop corresponding to theoverlap area 123 cA and the peak value of the pressure dropcorresponding to the overlap area 123 cC (step 1212 in FIG. 21). Thecontroller 170 obtains the positional shift amount Q from the detectionresult of the vacuum monitoring detector 146 corresponding to theoverlap area 123 cA and the teaching of the step 1106. Alternatively,the controller 170 may obtain the positional shift amount Q from thedetection result of the vacuum monitoring detector 146 corresponding tothe overlap area 123 cC and the teaching of the step 1106. Moreover, thecontroller 170 may obtain the positional shift amount Q by dividing by 2a sum of the positional shift amount Q from the detection result of thevacuum monitoring detector 146 corresponding to the overlap area 123 cAand the teaching of the step 1106, and the positional shift amount Qfrom the detection result of the vacuum monitoring detector 146corresponding to the overlap area 123 cC and the teaching of the step1106.

Next, the controller 170 drives the movement unit 160 so as to make zero(or reduce) this positional shift amount Q (step 1214). As a result, thecenter 17 a accords with the center J.

The number of grooves 123 is one in this embodiment, and the controller170 rotates the sleeve 121 and the bit 125 by 360° in the step 1212.When a plurality of grooves (such as four grooves 123) is used, thevacuum monitoring detector 146 is likely to detect a total of shifts ofthe respective grooves in FIG. 23 as each peak, each peak amount becomesequal, and a positional shift amount between the center axis 17 and Kmay not be recognized.

According to this embodiment, the center 17 a and the center J shift bythe positional shift amount Q in the lateral direction illustrated inFIG. 22, but when they shift in the longitudinal direction, thecontroller 170 recognizes the positional shift amount in thelongitudinal direction from a difference between the peak value of thepressure drop corresponding to the overlap area 123 cB and the peakvalue of the pressure drop corresponding to the overlap area 123 cD.

Referring now to FIGS. 24 to 28, a description will be given of anotherstructure used to achieve the flowcharts illustrated in FIGS. 20 and 21.FIG. 24 is a sectional view of a screwdriver 120B according to avariation of the structure illustrated in FIG. 3. The screwdriver 120Billustrated in FIG. 24 is different from the screwdriver 120 in that thescrewdriver 120B has no vacuum monitoring detector 146 and has anoptical sensor 148.

FIG. 25A is an enlarged sectional view of a lower portion of a sleeve121B. FIG. 25B is a bottom view of the sleeve 121B illustrated in FIG.25A. FIG. 26A is an enlarged sectional view of the lower portion of thesleeve 121B that has rotated clockwise by 45° from the rotationalposition illustrated in FIG. 25A. FIG. 26B is a bottom view of thesleeve 121B illustrated in FIG. 26A.

The sleeve 121B has an approximately hollow, cylindrical shape, andincludes an absorption hole (hollow part) 122 that can absorb the topsurface 16 of the screw 10, and a container 124 of the optical sensor148 as illustrated in FIG. 25B and 26B. The adsorption hole 122 issimilar to the absorption hole 122 illustrated in FIGS. 4 and 5. Thesleeve 121B has no groove 123 differently from the sleeve 121. Instead,the container 124 of the optical sensor 148 is provided.

The container 124 accommodates the optical sensor 148, as illustrated inFIG. 26A, has an L-shaped section, and includes a bottom open end 124 aand a side open end 124 b. The bottom open end 124 a has a circularopening on a bottom surface 121 aB of the sleeve 121B, and transmits thelight from the optical sensor 148. The bottom open end 124 a is smallerthan the optical sensor 148 so that the optical sensor 148 cannot dropfrom the bottom open end 124 a. The side open end 124 b opens on thecylindrical side surface 121 bB of the sleeve 121B, and allows the cable149 connected to the optical sensor 148 to pass through it. The size ofthe side open end 124 b is not limited.

FIG. 27A is a sectional view of the lower portion of the sleeve 121Bwhen the sleeve 121B is located close to the top surface 16 of the screw10 (at a distance of about 0.2 mm) FIG. 27B is a sectional view of FIG.27A viewed from an E2-E2 direction. FIG. 28A is a sectional view of thelower portion of the sleeve 121B located at a rotational position thatshifts by 45° from FIG. 27A. FIG. 28B is a sectional view of FIG. 28Aviewed from an F2-F2 direction. In FIGS. 27B and 28B, the center axis Kof the bit 125 or the sleeve 121 is aligned with the center axis 17 ofthe screw 10 in the vertical direction.

The bottom open end 124 a is separated from the absorption hole 122. Thebottom open end 124 a is formed on the bottom surface 121 aB of thesleeve 121B and opened to air. An angle is 45° between a line 124 a 1that connects a centerline of the bottom open end 124 a and the center Jin the radial direction, and the centerline 122 b 1 of the convex 122 bthat is closest to the bottom open end 124 a. With respect to the aboveline that connects a centerline of the bottom open end 124 a and thecenter J, the bottom open end 124 a is in a line symmetry.

When the bottom open end 124 a is viewed from the bottom surface 121 aBside of the sleeve 121B, the bottom open end 124 a at least partiallyprojects inside of a virtual circle C that passes the outermost diameterof the tip 125 a of the bit 125 around the center J. In this embodiment,the projection is connected to or disconnected from the recess 13according to the rotational position of the sleeve 121B. Due to thisstructure, the projection can be used as a detector. The bottom open end124 a may be entirely located inside of the circle C, but a function ofdetecting a positional shift between the centers 17 a and J may be lostin this case.

A variety of detectors of this embodiment uses no vacuum monitoringdetector 146, but uses the optical sensor 148. The optical sensor 148 ofthis embodiment is a reflection type photodetector, which can identifythe recess 13 from the top surface 16. The reflection type photodetectorincludes a light emitter and a light receiver, the light emitter uses anLED, and the light receiver uses a PD, a PTr, a photo IC, a modulationlight photo IC, etc. If necessary, a member that differentiates thereflectance may be adhered to the recess 13 or the top surface 16. Theoptical sensor 148 is connected to the cable 149, and the detectionresult of the optical sensor 148 is transmitted to the cable 149. Thecable 149 is connected with the controller 170.

FIGS. 27A and 27B illustrate that the phase of the dent 13 a of therecess 13 accords with the phase of the convex 122 b of the sleeve 121(or the projection 126 of the tip 125 a of the bit 125), and thecenterline 13 a 1 accords with the centerline 122 b 1. As illustrated inFIGS. 27A and 27B, when the bottom open end 124 a is disconnected fromthe recess 13, the optical sensor 148 detects the top surface 16 of thescrew 10.

On the other hand, FIGS. 28A and 28B illustrate that the phase (of thedent 13 a) of the recess 13 shifts by 45° from the phase (of the convex122 b) of the sleeve 121, and the centerline 13 a 1 that is one of fourdents 13 a accords with the centerline 122 a 1. As illustrated in FIGS.28A and 28B, when the bottom open end 124 a is located on the recess 13,the optical sensor 148 can identify the recess 13 at the projection 124c.

The configuration of this embodiment is applicable to the flowchartillustrated in FIGS. 10 to 12. In this case, the step 1210 illustratedin FIG. 12 may be replaced with “obtain information of a rotationalposition of the sleeve 121 (bit 125) when a line 124 a 1 that passes thecenterline of the bottom open end 124 a accords with the centerline 13 a1 of the dent 13 a of the recess 13 based on the detection result of theoptical sensor 148 and the detection result of the rotational positiondetector 144, and obtain a correction amount from teaching informationof the step 1102.”

In addition, as illustrated in the overlap areas 123 cA to 123 cD inFIG. 22, an area of the projection 124 c changes when there is apositional shift between the center 17 a and the center J. Therefore,the configuration of this embodiment is applicable to the flowchartillustrated in FIGS. 20 and 21.

In the step 1106 in FIG. 20, the controller 170 stores the teaching of arelationship between the positional shift amount and the light quantitydetected by the optical sensor 148 when an accordance between the center17 a and the center J (or the ideal state having a positional shiftamount of 0) is destroyed. Thereby, the controller 170 can obtain thedetection result of the optical sensor 148 and convert it into thepositional shift amount.

The “search position” in the step 1206 in FIG. 21 does not necessarilyrequire a “close” location as long as the optical sensor 148 is locatedat a detectable position of the shape of the top surface 16 of the screw10. The step 1212 in FIG. 21 is read in a different way as discussedabove. The controller 170 recognizes a positional shift amount from adifference between the light quantity corresponding to the area of theideal state of the projection 124 c and the light quantity correspondingto the real area. Next, the controller 170 drives the movement unit 160so as to make zero (or reduce) this positional shift amount (step 1214).Thereby, the center 17 a accords with the center J.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiment(s) of the presentinvention has (have) been described in detail, it should be understoodthat the various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

The present invention can provide a screw fastener configured to preventdamages of a bit and a recess, and a generation of the abrasion powder.

A screw fastener according to one aspect of the embodiment includes ascrewdriver that includes a sleeve having an absorption hole configuredto absorb a top surface of a screw, a bit housed in the absorption holeand having a tip engageable with a recess of the screw, and a rotationunit configured to rotate the bit with the sleeve, a movement unitconfigured to move the screwdriver between a container configured toaccommodate the screw and a work, a controller configured to controloperations of the screwdriver and the movement unit so as to pick up thescrew from the container and to fix a part onto the work with the screw,and a positional shift detector configured to detect a positional shifton a plane between a center axis of the screw perpendicular to the planeand a center axis of the bit perpendicular to the plane, wherein thecontroller controls a movement of the movement unit so as to reduce thepositional shift, based on a detection result of the positional shiftdetector. This screw fastener rotates the bit with the sleeve, and thuscauses less dust or fewer deformations than a screw fastener in whichthe screw is inserted into the absorption hole of the sleeve and thesleeve rotates but the sleeve is maintained stationary. Both center axesusually extend in the vertical direction (Z-axis direction) and theplane perpendicular to both axes is an XY plane. The controller controlsthe movement unit so that the center axis of the bit of the screwdrivercan accord with the center axis of the recess of the screw (idealstate). However, the ideal state in which a positional shift betweenboth center axes is zero is not always obtained. Accordingly, apositional shift detector detects an actual positional shift betweenboth center axes on the XY plane, and the controller calibrates a shiftbetween the ideal state and the real state by controlling the movementunit based on the detection result. As a result, when the bit is engagedwith the recess of the screw, the dust generations and the damages ordeformations of the bit and the screw reduce. The reduced dustgenerations provide effects of eliminating or reducing pollution andelectric short circuit of the product, and the reduced deformationsprovide effects of eliminating or reducing defective screw fasteningwith a predetermined torque, defective products, or extra tool exchangeprocesses. Moreover, since it is unnecessary to align the phase of therecess of the screw beforehand, an installation operation of the screwbecomes easier.

The positional shift detector may include a pressure detector configuredto detect a pressure in the absorption hole, and a groove configured toconnect the absorption hole to and disconnect the absorption hole fromair external to the sleeve according to a rotational position of thesleeve. Thereby, a positional shift that cannot be seen between bothcenter axes can be measured with a simple structure. In addition, byconnecting the absorption hole to the external air according to therotational position of the sleeve, the pressure fluctuationcorresponding to the position shift between both center axes can becreated with a simple structure. The groove may be provided on a bottomsurface of the sleeve or provided on the top surface of the screw.

The positional shift detector may include a pressure detector configuredto detect a pressure in the absorption hole, and a groove provided on abottom surface of the sleeve, separated from the absorption hole, andopened to air. The controller may rotate the sleeve and the bit via therotation unit while the bottom surface of the sleeve and the top surfaceof the screw are being maintained in a noncontact manner. In addition,the controller may obtain the positional shift amount from the pressuredetector based on a relationship between the positional shift amount onthe plane and the pressure and a detection result of the pressuredetector. Moreover, when the sleeve is viewed from a bottom surfaceside, the groove projects inside of a virtual circle that passes anoutermost diameter of the tip of the bit around a center as the centeraxis of the bit. This structure converts the positional shift betweenboth center axes into a pressure fluctuation of the absorption hole inthe sleeve, and enables the positional shift between both center axes tobe detected with a simple structure. There may be only one groove, andthe controller may rotate the sleeve and the bit by 360°. This isbecause if a plurality of grooves is used, the pressure detector detectsa total of shifts of the respective grooves and a positional shiftamount may not be recognized.

The absorption hole may be smaller than a screw head of the screw.Thereby, the dust generations and the deformations reduce in comparisonwith a screw fastener in which the screw is inserted into the absorptionhole of the sleeve and the sleeve rotates but the sleeve is maintainedstationary.

The screw fastener may further include a sleeve holder having a centralperforation hole connected to the absorption hole and configured toaccommodate the sleeve rotatably, and a vacuum drawer configured to drawa vacuum in the absorption hole. The vacuum drawer includes a suctionplug attached to a side perforation hole provided in a side surface ofthe sleeve holder and connected to the central perforation hole,maintained stationary with the sleeve holder when the sleeve rotateswith the bit, and configured to draw a vacuum in the absorption holethrough the side perforation hole and the central perforation hole.Since the suction plug does not rotate even when the bit rotates, anarrangement of the tube connected to the suction plug becomes easier.

1. A screw fastener comprising: a screwdriver that includes a sleevehaving an absorption hole configured to absorb a top surface of a screw,a bit housed in the absorption hole and having a tip engageable with arecess of the screw, and a rotation unit configured to rotate the bitwith the sleeve; a movement unit configured to move the screwdriverbetween a container configured to accommodate the screw and a work; acontroller configured to control operations of the screwdriver and themovement unit so as to pick up the screw from the container and to fix apart onto the work with the screw; and a positional shift detectorconfigured to detect a positional shift on a plane between a center axisof the screw perpendicular to the plane and a center axis of the bitperpendicular to the plane, wherein the controller controls a movementof the movement unit so as to reduce the positional shift, based on adetection result of the positional shift detector.
 2. The screw fasteneraccording to claim 1, wherein the positional shift detector includes: apressure detector configured to detect a pressure in the absorptionhole; and a groove configured to connect the absorption hole to anddisconnect the absorption hole from air external to the sleeve accordingto a rotational position of the sleeve.
 3. The screw fastener accordingto claim 2, wherein the groove is provided on a bottom surface of thesleeve.
 4. The screw fastener according to claim 2, wherein the grooveis provided on the top surface of the screw.
 5. The screw fasteneraccording to claim 1, wherein the positional shift detector includes: apressure detector configured to detect a pressure in the absorptionhole; and a groove provided on a bottom surface of the sleeve, separatedfrom the absorption hole, and opened to air, wherein the controllerrotates the sleeve and the bit via the rotation unit while the bottomsurface of the sleeve and the top surface of the screw are beingmaintained in a noncontact manner, wherein the controller obtains thepositional shift amount from the pressure detector based on arelationship between the positional shift amount on the plane and thepressure and a detection result of the pressure detector, and whereinwhen the sleeve is viewed from a bottom surface side, the grooveprojects inside of a virtual circle that passes an outermost diameter ofthe tip of the bit around a center as the center axis of the bit.
 6. Thescrew fastener according to claim 5, wherein there is only one groove,and the controller rotates the sleeve and the bit by 360°.
 7. The screwfastener according to claim 1, wherein the absorption hole is smallerthan a screw head of the screw.
 8. The screw fastener according to claim1, further comprising: a sleeve holder having a central perforation holeconnected to the absorption hole and configured to accommodate thesleeve rotatably; and a vacuum drawer configured to draw a vacuum in theabsorption hole, wherein the vacuum drawer includes a suction plugattached to a side perforation hole provided in a side surface of thesleeve holder and connected to the central perforation hole, maintainedstationary with the sleeve holder when the sleeve rotates with the bit,and configured to draw a vacuum in the absorption hole through the sideperforation hole and the central perforation hole.